Drawing a good free-body diagram (FBD) is generally acknowledged by mechanics instructors as a critical step in solving mechanics problems. In this paper we will summarize recommended procedures and mnemonics that have been developed to help students draw good FBDs. In spite of the fact that every Statics book we examined presented a step-by-step procedure for drawing free-body diagrams, they all included what the authors consider to be poor practices that can lead to misconceptions and difficulties when students take Dynamics. We will discuss these pitfalls in Statics textbooks, show examples from popular Statics textbooks that illustrate them, and discuss how the consistent use of effective FBD drawing strategies can be used to avoid them. We surveyed experienced instructors who use free-body diagrams and asked them to rate, in their opinion, the importance of each element of a FBD we identified from the procedures presented in Statics books, and we also asked them to choose between two mnemonics for drawing FBDs: “The ABC’s of FBD’s” and “BREAD.” We found that, in general, faculty members agreed on most of the elements, although there was no consensus on the importance of including dimensions on a FBD. Of the mnemonics, 57% of the respondents preferred “BREAD,” 24% preferred “The ABC’s of FBD’s,” and 19% had no preference.
Phillip Cornwell currently teaches at the United States Air Force Academy and is an Emeritus Professor of Mechanical Engineering at Rose-Hulman Institute of Technology. He received his Ph.D. from Princeton University in 1989 and his present interests include structural dynamics, structural health monitoring, and undergraduate engineering education. Dr. Cornwell has received an SAE Ralph R. Teetor Educational Award in 1992, and the Dean’s Outstanding Teacher award at Rose-Hulman in 2000 and the Rose-Hulman Board of Trustee’s Outstanding Scholar Award in 2001. He was one of the developers of the Rose-Hulman Sophomore Engineering Curriculum, the Dynamics Concept Inventory, and he is a co-author of Vector Mechanics for Engineers: Dynamics, by Beer, Johnston, Cornwell, and Self. In 2019 Dr. Cornwell received the Archie Higdon Distinguished Educator Award from the Mechanics Division of ASEE.
Dr. Danesh-Yazdi is Assistant Professor of Mechanical Engineering at Rose-Hulman Institute of Technology.
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